RESUMO
This paper presents a new method to reduce halo artifacts in Computed Tomography (CT) images, which blur the image edges and descend the image quality. Off-focal radiation is main ill factor leading to these halo artifacts. To reduce the off-focal effects, we adopt a pre-processing method to filter the sampling data directly before reconstruction, instead of post-processing method such as edge enhancing on the reconstructed images. Different from the prior pre-processing method, we also present a new and more practical method to obtain convolution kernel and a simpler formula in this paper. Results show that after calibration by the new practical method, the off-focal radiation effects were reduced efficiently, the edges were enhanced and the image quality was improved without increasing noise.
RESUMO
This work presents a new method to reduce nonlinear artifacts in computed tomography (CT). Based on the traditional water-equivalent beam hardening correction method, a new systematic iterative algorithm has been designed to modify the original spectrum, which is under the influences of certain added filter materials and some unknown factors. By incorporating the characters of polychromatic beam hardening and the insensibility and nonuniformity of detectors into consideration, a new polynomial function curve is calculated. The curve can calibrate CT raw data and reduce the nonlinear artifacts, such as shading artifacts, dark artifacts, cupping artifacts and ring artifacts, in soft tissue. Comparing with the traditional water-equivalent correction, results show that this method can significantly improve the image quality. Meanwhile, the method is pre-processing and will not increase the normal reconstruction time. That is, all the time-consuming works can be done before scanning patients. However, it is still depending on the size of phantoms currently used, and more detailed works need to be done in the future.